Method and device for controlling beginning point of optical pick-up unit

ABSTRACT

A method and device are provided for controlling movement of an optical pick-up unit. The method includes a) moving the optical pick-up unit toward a target position of an optical disc; b) while the optical pick-up unit is in motion, detecting a load voltage of a driver for moving the optical pick-up unit and detecting a counted value of the driver&#39;s output pulses generated as the driver is activated; and c) determining whether the optical pick-up unit having been moved is positioned at a beginning point of the optical disc on the basis of a current load voltage of the driver and the counted value of the drive&#39;s output pulses.

The Divisional application is a Divisional of co-pending U.S. PatentApplication No. 10/684,448 filed Oct. 15, 2003, which is incorporated byreference. The present application also claims, under 35 U.S.C. § 119,the priority benefit of Korean Patent Application No. 2002-62936 filedOct. 15, 2002 and Korean Patent Application No. 2002-72511filed Nov. 20,2002, the entire contents of which are herein fully incorporated byreference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a method and device for controlling abeginning point of an optical pick-up unit, and more particularly to amethod and device for moving the optical pick-up unit to a beginningpoint of an optical disc such as a DVD (Digital Versatile Disc) in orderto execute a servo-tuning function.

2. Description of the Related Art

FIG. 1 is a block diagram of a conventional optical disc driver such asa DVD player. Referring to FIG. 1, the conventional DVD player includesan optical pick-up unit 20 for reading/writing data from/to an opticaldisc 10 such as a DVD, a spindle motor 21 for rotating the disc 10, asled motor 22 for moving the optical pick-up unit 20 to an inner orouter portion of the disc 10, a limit switch 23 for generating a lowsignal L when the optical pick-up unit 20 moves to the innermost datatrack of the disc 10, a RF unit 30 for filtering an output signal of theoptical pick-up unit 20 to create a binary signal, and a DSP (DigitalSignal Processor) 40 for restoring the binary signal to original dataaccording to its own clock being phase-locked with the binary signal.

The conventional DVD player further includes an MPEG decoder 50 fordecoding the restored data generated from the DSP 40 according to anMPEG scheme, a motor drive 60 for applying a proper drive voltage to thespindle motor 21 and the sled motor 22, rotating the disc 10 and slidingthe optical pick-up unit 20, and a microcomputer 70 for determining acurrent position of the optical pick-up unit 20 based on an outputsignal from the limit switch 23, and performing a servo-tuningoperation.

Typically, if the disc 10 is inserted into the DVD player shown in FIG.1, the microcomputer 70 executes a servo-tuning function to read thedisc 10. In this case, the microcomputer 70 controls the optical pick-upunit 20 to be located at an innermost data track (also called abeginning point) of the disc 10, and then executes a servo-tuningoperation. However, since the microcomputer 70 is unable to recognize acurrent position of the optical pick-up unit 20 before reading the disc10, it firstly moves the optical pick-up unit 20 to the beginning point(i.e., the innermost data track) of the disc 10 prior to executing theservo-tuning operation. This operation will hereinafter be described inmore detail.

If the disc 10 is inserted into the DVD player, the microcomputer 70applies a proper drive voltage to the sled motor 22, and moves theoptical pick-up unit 20 to the beginning point (i.e., innermost datatrack) of the disc 10. In this case, the limit switch 23 outputs thesignal L when the optical pick-up unit 20 is placed at the innermostdata track of the disc 10, such that the microcomputer 70 continuouslychecks the output signal of the limit switch 23 while the opticalpick-up unit 20 is in motion in order to determine whether the opticalpick-up unit 20 has been moved to the innermost data track.

When the optical pick-up unit 20 finally moves to the innermost datatrack, the microcomputer 70 executes a prescribed servo-tuningoperation.

However, the aforementioned conventional DVD player must adapt anadditional limit switch to determine whether the optical pick-up unit 20has been moved to the innermost data track of the disc 10, resulting inthe increase of size and cost of the DVD player.

SUMMARY OF THE INVENTION

Therefore, the present invention has been made in view of the aboveproblems.

It is an object of the present invention to provide a method and devicefor controlling a beginning point of an optical pick-up unit in order tomove the optical pick-up unit to a beginning point of an optical discwithout using an additional component such as a limit switch, such thatit performs a servo-tuning operation at the innermost data track of theoptical disc.

In accordance with one aspect of the present invention, the above andother objects can be accomplished by the provision of a method forcomprising the steps of: a) performing a focus search operation on anoptical disc and at the same time determining whether there is areflection signal from the optical disc; b) after performing the focussearch operation, moving the optical pick-up unit toward a predeterminedbeginning point of the optical disc based on the result of thedetermining step; and c) based on the reflection signal from the opticaldisc, determining whether or not the optical pick-up unit has moved tothe beginning point of the optical disc while the optical pick-up unitis in motion.

In accordance with another aspect of the present invention, there isprovided a method for controlling movement of an optical pick-up unit,comprising the steps of: a) moving the optical pick-up unit toward atarget position of an optical disc; b) while the optical pick-up unit isin motion, detecting a load voltage of a driver for moving the opticalpick-up unit and detecting a counted value of the driver's output pulsesgenerated as the driver is activated; and c) determining whether theoptical pick-up unit having been moved is positioned at a beginningpoint of the optical disc on the basis of a current load voltage of thedriver and the counted value of the drive's output pulses.

These and other objects of the present application will become morereadily apparent from the detailed description given hereinafter.However, it should be understood that the detailed description andspecific examples, while indicating preferred embodiments of theinvention, are given by way of illustration only, since various changesand modifications within the spirit and scope of the invention willbecome apparent to those skilled in the art from this detaileddescription.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other objects, features and other advantages of thepresent invention will be more clearly understood from the followingdetailed description taken in conjunction with the accompanyingdrawings, in which:

FIG. 1 is a block diagram of a conventional optical disc driver;

FIG. 2 is a block diagram of an optical disc driver to which a methodfor controlling a beginning point of an optical pick-up unit inaccordance with a first preferred embodiment of the present invention isapplied;

FIG. 3 is an exemplary view illustrating an initial position B of anunmoved optical pick-up unit and an innermost data track A of a disc;

FIGS. 4 a and 4 b are flow charts illustrating a method for controllinga beginning point of an optical pick-up unit in accordance with thefirst preferred embodiment of the present invention;

FIG. 5 is a block diagram of an optical disc driver to which a methodfor controlling a beginning point of an optical pick-up unit inaccordance with a second preferred embodiment of the present inventionis applied;

FIG. 6 is an exemplary view illustrating a block diagram of a sled motordrive using a microcomputer and a motor drive in accordance with thesecond preferred embodiment of the present invention;

FIG. 7 is an exemplary graph illustrating the difference between a loadvoltage of a sled motor at a normal rotation state and a load voltage ofthe sled motor at an extreme position control state; and

FIG. 8 is a flow chart illustrating a method for controlling a beginningpoint of an optical pick-up unit in accordance with the second preferredembodiment of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Now, preferred embodiments of the present invention will be described indetail with reference to the annexed drawings. In the drawings, the sameor similar elements are denoted by the same reference numerals eventhough they are depicted in different drawings. In the followingdescription, a detailed description of known functions andconfigurations incorporated herein will be omitted when it may make thesubject matter of the present invention unclear.

FIG. 2 is a block diagram of an optical disc driver to which a methodfor controlling a beginning point of an optical pick-up unit inaccordance with a first preferred embodiment of the present invention isapplied. In comparison with the conventional optical disc driver, theoptical disc driver shown in FIG. 2 does not include a limit switchwhereas the conventional optical disc driver includes the limit switch23. But the remaining components of the present disc driver, other thanthe limit switch, are the same as those of the conventional DVD playershown in FIG. 1. All the components of the optical disc driver in FIG. 2are operatively coupled. The methods of the present invention are alsoapplicable to other types of disc drivers.

FIGS. 4 a and 4 b are flow charts illustrating a method for controllinga beginning point of an optical pick-up unit in accordance with thefirst preferred embodiment of the present invention. The method shown inFIGS. 4 a-4 b will hereinafter be described in more detail withreference to FIG. 2.

First, if a tray with a disc 10 is inserted into an optical disc (e.g.,as shown in FIG. 2) driver at step S10, a microcomputer 70 applies aproper voltage to an LD (Laser Diode) (or other light source) of anoptical pick-up unit 20 over an RF unit 30, such that the LD is turnedon. An objective lens of the optical pick-up unit 20 performs a focussearch function to focus on a signal surface (i.e., recording surface)of the disc 10 at step Sll, and it is determined at step S12 whetherthere is a reflection signal from the disc 10.

If it is determined at step S12 that there is the reflection signal fromthe disc 10, that is, if a focus servo is switched on, the microcomputer70 performs a beginning point control function to execute a servo-tuningoperation on the disc 10 inserted into the optical disc driver. For thispurpose, the microcomputer 70 moves the optical pick-up unit 20 to theinnermost data track being a beginning point on the disc 10 while theDSP 40 holds a focus drive signal applied to the motor drive 60 at stepS13.

Generally, as shown in FIG. 3, in the case of inserting the disc 10 intothe optical disc driver, the optical pick-up unit 20 is positioned at arandom point B between the innermost data track A and an outermost datatrack of the disc 10. Therefore, considering this situation, themicrocomputer 70 applies a certain proper drive voltage to the sledmotor 22 through the motor drive 60, to move the optical pick-up unit 20according to the applied drive voltage from the beginning point Btowards the innermost data track A of the disc 10 having a diameter of12cm at step S13.

While the optical pick-up unit 20 is in motion, the microcomputer 70determines whether the optical pick-up unit 20 is currently positionedat the innermost data track of the disc 10 on the basis of thereflection signal from the disc 10, and this determination process willhereinafter be described in detail.

While the optical pick-up unit 20 is in motion, the microcomputer 70continuously checks a PI (Pull In Error) signal (or an AS signal)generated from the RF unit 30 receiving the reflection signal from thedisc 10 at step S14. In this case, the PI signal is generated by the RFunit 30 converting an optical signal from the optical pick-up unit 20into a DC value.

If the optical pick-up unit 20 is positioned at the innermost data trackof the disc 10 while the focus servo is switched on, the level of the PIsignal (or an AS signal) drops down to less than a predetermined level.If this happens, the microcomputer 70 determines that the opticalpick-up unit 20 has moved to the innermost data track of the disc 10 atstep S20. Otherwise, the process repeats steps S13, S14 and S20 untilthe optical pick-up unit 20 is moved to the innermost data track of thedisc 10.

In this way, if it is determined at step S20 that the optical pick-upunit 20 has moved to the innermost data track of the disc 10, themicrocomputer 70 stops the above beginning point control operation, andperforms a servo-tuning operation at step S21. Therefore, a normaloperation such as reading the disc 10 can be performed.

In addition, the microcomputer 70 is able to determine the type of theinserted disc 10. For example, in the case where a disc with a diameterof 8cm is inserted into the optical disc driver and a beginning point Bof the optical pick-up unit 20 is set to be outside of the perimeter ofa general disc with a diameter of 8cm as shown in FIG. 3, themicrocomputer 70 is able to determine the type of the inserted disc uponreceiving the reflection signal from the

For instance, if a disc 10 is inserted into the optical disc driver atstep S10, the microcomputer 70 performs a focus search operation at theset beginning point B of the optical pick-up unit 20 at step S11. Inthis case, if the inserted disc 10 is not a disc with a diameter of 12cmor if the inserted disc 10 has a diameter greater than at least 8cm,there will be no reflection signal at the point B at step S12. Then, themicrocomputer 70 determines that the optical pick-up unit 20 iscurrently outside of a disc having a diameter of 8cm and the inserteddisc 10 has a diameter of 8cm. In order to confirm this determination,the microcomputer 70 moves the optical pick-up unit 20 by a prescribeddistance in such a way that the optical pick-up unit 20 is positionedover or in the vicinity of a point C for an 8cm-diameter disc as shownin FIG. 3 at step S15. Herein, a division of a method for controlling abeginning point of the optical pick-up unit 20 in accordance withanother preferred embodiment of the present invention to be explainedbelow can be adapted to step S15. That is, the optical pick-up unit 20can move by the prescribed distance by executing step S30 to S40 of FIG.8. In this case, a counter 71 as shown in FIG. 5 would be needed, whichwill be discussed later.

After step S15, the microcomputer 70 re-executes the above focus searchoperation at step S16 while the optical pick-up unit 20 is in thevicinity of the point C of the disc 10, and determines whether there isa reflection signal from the disc 10 at step S17. In the case wherethere is the reflection signal from the disc 10 and the focus servo isturned on while the microcomputer 70 executes the focus searchoperation, the microcomputer 70 determines that the inserted disc 10 hasa diameter of 8cm at step S18. Then, in the case where the focus servois turned on, the process returns to step S13 wherein the microcomputer70 moves the optical pick-up unit 20 to the innermost data track A ofthe 8cm-sized disc 10 in order to perform a servo tuning operation atstep S13.

In the case where there is no reflection signal from the disc 10 whilethe microcomputer 70 executes the focus search operation, themicrocomputer 70 determines that the disc is not inserted into theoptical disc driver at step S19, and thereby terminates a program.

Although the process of determining the type of an inserted disc hasbeen discussed above for discriminating between a disc having a 12cmdiameter and a disc having an 8cm diameter, the present inventionencompasses discriminating between discs having other diameters. Thiscan be accomplished by setting the point B and any additional pointsbased on such disc sizes. For instance, to discriminate between a discof 12cm diameter and a disc of 10cm diameter, the point B of FIG. 3 canbe set to be outside of the range of a general disc with the 10cmdiameter.

A method for controlling a beginning point of the optical pick-up unit20 in accordance with a second preferred embodiment of the presentinvention will hereinafter be described with reference to FIGS. 5 to 8,in which the microcomputer 70 determines conditionally or periodicallywhether the optical pick-up unit 20 has reached the innermost data trackof the disc 10 while the optical pick-up unit 20 is being moved towardthe target position (e.g., innermost data track) of the disc 10.

FIG. 5 is a block diagram of an optical disc driver to which a methodfor controlling a beginning point of the optical pick-up unit 20 inaccordance with the second preferred embodiment of the present inventionis applied. In comparison with the conventional DVD player shown in FIG.1, the optical disc driver shown in FIG. 5 does not include a limitswitch whereas the conventional optical disc driver includes the limitswitch 23. But, the driver of FIG. 5 includes a counter 71 for countingoutput pulses (e.g., step pulses) of the sled motor 22 while rotatingthe sled motor 22. The remaining components of the driver in FIG. 5,other than the limit switch, are the same as those of FIG. 1. All thecomponents of the optical disc driver in FIG. 5 are operatively coupled.

FIG. 6 is an exemplary view illustrating a block diagram of a sled motordrive 22 using the microcomputer 70 and a motor drive 60 in FIG. 5.

FIG. 8 is a flow chart illustrating a method for controlling a beginningpoint of an optical pick-up unit in accordance with the second preferredembodiment of the present invention. The method shown in FIG. 8 willhereinafter be described with reference to FIGS. 5 and 6.

First, provided that a distance by which the optical pick-up unit 20 isto move is predetermined to reach the target position such as theinnermost data track of the inserted disc, the microcomputer 70 controlsthe optical pick-up unit 20 to move by this distance when a disc isinserted, and at the same time experimentally sets up the number (targetvalue) of output pulses for the sled motor 22. Then, number (n) ofoutput pulses (i.e., step pulses generated by the rotation of the motor22) from the sled motor 22 is counted as the sled motor 22 rotates tomove the pick-up unit 20 until the optical pick-up unit 20 moves by thepredetermined distance, i.e., when the counted output pulse numberreaches the target output pulse number.

More specifically, referring to FIG. 8, when a desired moving distanceof the optical pick-up unit 20 is predetermined and a moving command areset up at step S30, the microcomputer 70 sets up the desired number ‘m’(target value) of output pulses for the sled motor 22 at step S31according to the predetermined moving distance. Thereafter, as shown inFIG. 6, the microcomputer 70 applies a proper drive voltage to the sledmotor 22 through the motor drive 60, rotates the sled motor 22, and thusbegins moving the optical pick-up unit 20 from a current position towarda target position (e.g., innermost data track) at step S32. While theoptical pick-up unit 20 is in motion, the counter 71 counts the numberof output pulses (i.e., step pulses) generated by the rotation of thesled motor 22 at step S33, and transmits the counted number n to themicrocomputer 70. Therefore, the microcomputer 70 continuously detectsthe counted number and compares this counted number with thepredetermined target number ‘m’ at step S40, and continuously moves theoptical pick-up unit 20 until the counted number ‘n’ reaches (orexceeds) the predetermined target number ‘m’. In this case, if theoptical pick-up unit 20 is close to the innermost data track of the disc10, the load voltage of the sled motor 22 will abruptly increase. Inmore detail, in the case of an extreme position control state shown inFIG. 7 (such as being positioned at the innermost data track of thedisc), the load voltage of the sled motor 22 increases from a loadvoltage ‘d’ in a normal rotation state to a prescribed voltage ‘d+e’.This ‘d+e’ voltage (or the allowable range for this abrupt increase inthe load voltage from the normal rotation state) can be experimentallydetermined in advance, and is used at step S50 as a prescribed(reference) load voltage (or voltage range) indicative that the pick-upunit 20 has reached the innermost data track of the inserted disc.

That is, if it is determined at step S40 that the counted number ‘n’ isbeyond the predetermined target number ‘m’, the microcomputer 70 detectsa load voltage of the sled motor 22 at step S41, and compares thedetected load voltage with the prescribed load voltage discussed above.If it is determined at step S50 whether the detected load voltage is ina predetermined allowable range on the basis of the prescribed value,the microcomputer 70 determines that the optical pick-up unit 20 hasbeen moved to the innermost data track of the disc 10 at step S51. But,if it is determined at step S50 that the load voltage is not in thepredetermined allowable range on the basis of the prescribed value, themicrocomputer 70 determines that the optical pick-up unit 20 is notcurrently positioned at the innermost data track of the disc 10 at stepS52. In this case, the process may end or the microcomputer 70 can applya proper drive voltage to the sled motor 20 to continue to move thepick-up unit 20 until the pick-up unit 20 reaches the innermost datatrack. The load voltage can be checked continuously to determine whetheror not the pick-up unit 20 has reached the innermost data track (e.g.,steps S41 and S50 may be performed repeatedly). Other variations arepossible.

After step S51, step S21 of FIG. 4a can be performed.

As apparent from the above description, a method for controlling abeginning point of an optical pick-up unit according to the presentinvention moves the optical pick-up unit to a beginning point (i.e.,innermost data track) of a disc based on a reflection signal from thedisc without using an additional limit switch, in such a way that itreduces the volume and cost of an optical disc driver, determines thetype of the disc, and determines whether the disc is inserted into theoptical disc driver.

Although the preferred embodiments of the present invention have beendisclosed for illustrative purposes, those skilled in the art willappreciate that various modifications, additions and substitutions arepossible, without departing from the scope and spirit of the inventionas disclosed in the accompanying claims.

1. A method for controlling movement of an optical pick-up unit,comprising: a) moving the optical pick-up unit toward a target positionof an optical disc; b) while the optical pick-up unit is in motion,detecting a load voltage of a driver for moving the optical pick-up unitand detecting a counted value of the driver's output pulses generated asthe driver is activated; and c) determining whether the optical pick-upunit having been moved is positioned at a beginning point of the opticaldisc on the basis of a current load voltage of the driver and thecounted value of the drive's output pulses.
 2. The method as set forthin claim 1, wherein the step (c) includes: Cl) comparing the currentload voltage of the driver with a prescribed load voltage to determinewhether the optical pick-up unit is positioned at the beginning point ofthe optical disc.
 3. The method as set forth in claim 1, wherein thebeginning point of the optical disc is an innermost data track of theoptical disc.
 4. The method as set forth in claim 1, further comprising:d) if the optical pick-up unit has moved to the beginning point of theoptical disc, performing a servo-tuning operation.
 5. The method as setforth in claim 1, wherein in the step (b), the driver's output pulsesare step pulses generated from a rotation of a sled motor being thedriver.
 6. A device for controlling movement of an optical pick-up unit,comprising: first means for moving the optical pick-up unit toward atarget position of an optical disc; while the optical pick-up unit is inmotion, second means for detecting a load voltage of a driver for movingthe optical pick-up unit and detecting a counted value of the driver'soutput pulses generated as the driver is activated; and third means fordetermining whether the optical pick-up unit having been moved ispositioned at a beginning point of the optical disc on the basis of acurrent load voltage of the driver and the counted value of the drive'soutput pulses.
 7. The device as set forth in claim 6, wherein the thirdmeans compares the current load voltage of the driver with a prescribedload voltage to determine whether the optical pick-up unit is positionedat the beginning point of the optical disc.
 8. The device as set forthin claim 6, wherein the beginning point of the optical disc is aninnermost data track of the optical disc.
 9. The device as set forth inclaim 6, further comprising: fourth means for performing a servo-tuningoperation if the optical pick-up unit has moved to the beginning pointof the optical disc.
 10. The device as set forth in claim 6, wherein thedriver's output pulses are step pulses generated from a rotation of asled motor being the driver.